Heretofore, there have been proposed various types of rich-lean combustion burners. In such a type of rich-lean combustion burner, a lean-side mixture the air ratio of which is in excess of 1.0 is burned at lean-side flame holes for the accomplishment of NOx reduction, while for the stabilization of combustion flames, rich-side flame holes where a rich-side mixture the air ratio of which is below 1.0 is burned are arranged adjacent to the lean-side flame holes. And, as such a rich-lean combustion burner, there has been proposed a rich-lean combustion burner which is formed in the form of a flat shape as a whole by joining or welding together thin plate members formed into their predetermined shapes by means of press forming or other like forming means (see, for example, Patent Literature Publications 1 and 2).
Especially, Patent Literature Publication 1 proposes that work improvement in the cutting process to be performed on individual members as well as in the joining/welding process to be performed on the individual members is accomplished by performing bending of a single sheet of thin material for more than once. In addition, Patent Literature Publication 2 proposes that the sealability is ensured by means of concavity/convexity fitting of ribs instead of the aforesaid surface-to-surface joint.